Objectives: S.W.B.A.T.

Understand the classification of stars – spectral class

Label stages of an average main sequence star to an H-R diagram

Define/describe stages the of the sun’s life cycle from birth to death

Activities:

Warm-up

Finish video spectrum light color

Notes/discussion

Microslide review - sun

Spectral classification of stars

Stars are classified by the temperature and the element spectral lines found in the star. Classified by letters and numbers

O B A F G K M “oh be a fine girl/guy kiss me”

Each has 10 sub categories numbers from 0 to 9

The size and brightness is also classified by Roman numbers/letters

Ia – Bright Supergiants Ib – Supergiants II – Bright Giants III – Normal Giants IV – Subgiants V – Main Sequence Our sun is classified as a G2V

Life of the sun / Evolution of Stars

Stage 1 Nebula – a huge cloud of gas & dust mostly of hydrogen collects and contracts due to gravity. 2-5 billion years

100 trillion-1 billion km in diameter (light years across)

Stage 2 Protostar – prestart that is not hot enough to shine in visible light (shines in radio waves to infrared energy) size ranges from 300,000 X of solar system to 10,000 X diameter of the sun.

-time span last around 100,000 years

Stag 3 T-Tauri – a class of variable star prior to main sequence, 1st discovered in constellation in Taurus. Stars are the same mass, as main sequence, but they are significantly more luminous because their radii are larger. Temperature in core is to low for nuclear fusion.

Powered by gravitational energy. (Size rage: 1000 X diameter of sun) last in this stage ~ 100 million years

Stage 4 Main Sequence – “Star Birth” nuclear fusion inside star core begins makes star hot enough to shine. Converts H He in the proton-proton cycle. 90% of stars are main sequence stage. Stars are said to be in Hydrostatic Equilibrium: energy output = gravitational pull inward (known as hydrogen burning stage)

Stars like our sun last 10 billion years as a main sequence

ZAMS –zero age main sequence

Step 4 Helium Flash / Red Giant – as hydrogen in core of star decreases and helium in core rises, the star starts to become unstable and equilibrium breaks down, gravity takes over – causing greater pressure on core and causes helium flash or fusion (new energy He C ) Star grows: increase energy overcomes gravity, star moves off the main sequence to red giant area of graph.

**All stars go through Red Giant or Red Super Giant stage

Stage 5 Planetary Nebula / Nova - star uses up most of He and moves back toward main sequence area of H-R diagram.

Star fluctuates on and off main sequence. Gravity tries to contact star creating other elements in star increasing fusion process.

This increase energy causes an explosion-like occurrence. This cause star to lose large quantities of mass.

Also during this time period star sheds off excess gas envelopes, which appears as a ring around star when viewed from a distance.

Stage 6 White Dwarf – Star continues the fusion process He to C, and C to O and Ne, O, to Si. Star burns hot due to gravitational pressure. The average white dwarf is about the size of a large planet.

Stage 7 Black Dwarf – final stage of a low mass main sequence star. All fusion stops core dies out no fuel. What remains is a dense silicon rock ~ 90% +/- of the original stars mass.

The stages of a stars evolution can be plotted on a graph that shows temperature (K) vs. Brightness absolute magnitude or luminosity: solar units)

Graph is known as the Hertzsprung – Russel diagram H-R diagram

(One of the most important charts in astronomy)

http://www.google.com/search?q=Heinrich+Rudolf+Hertz&ct=hertz-2011-hp&oi=ddle